錳砂濾料之抗菌性研究

Abstract

過濾是給水廠不可或缺之程序，但此過濾效能會因有機及無機物質存在(懸浮顆粒、藻類及有機物質)致堵塞濾床後而變差。於過濾期間，一旦生物膜聚集於濾料表面，過濾之能力及濾程將會明顯地降低並伴隨著高頻率之反洗，因此，如何延遲微生物於砂濾程序中的生長能力是重要之關鍵因素。 石英砂是一種於給水廠過濾程序中常用之氧化矽濾料，然而於過濾程序中石英砂易因微生物附著致生物膜快速發展，進而堵塞濾床。另一方面，多種金屬氧化物(如TiO2, ZnO, MnO2)已被證明於富含營養源之環境中具有抑制生物膜聚集之能力，而可成為抗生物生長之材料。於水處理過程，錳砂濾料表面MnO2氧化物並被廣泛適用於移除地下水中之鐵、錳離子，但錳砂之抗菌能力仍有待更進一步的研究。 本研究評估高錳酸鉀有無活化錳砂後之抗菌性並與石英砂相互比較，再者，探討高錳酸鉀及次氯酸鈉氧化活化錳砂之抗菌性。實驗室配製含菌(E. coli)水與表層天然水為實驗用水，並以(Luria-Bertani, LB)作為額外添加之培養基質。試驗條件以恆溫37℃培養48 hr，殘餘菌數利用光學密度法(OD)及DAPI (4',6-diamidino-2-phenylindole)染色法分析。 研究結果顯示錳砂之抗菌性優於石英砂，以高錳酸鉀活化錳砂後增加了活性MnO2顆粒物量及提高其表面積，進而減緩了微生物生長速度。此外，水溶液之氧化還原電位(ORP)會因殘餘菌體數變少而升高。在含錳砂之培養液中，因微生物的失活而釋出鉀離子，而高錳酸鉀活化錳砂之殘餘鉀離子濃度又高於未活化之錳砂。隨著活化錳砂總量之增加，鉀離子濃度會因殘餘微生物量之降低而增加，且殘餘微生物量在12小時內大幅度減少。另一方面，高錳酸鉀或次氯酸鈉氧化劑不僅可先破壞水體中之微生物，亦可增加活化錳砂之二氧化錳含量，致水體中殘餘之微生物量減少。然而，由於高錳酸鉀氧化使微生物失活之能力強且可生成二氧化錳之含量又高於次氯酸鈉氧化，故高錳酸鉀氧化是提昇錳砂抗菌性之最佳方法。本研究結果顯示，飲用水處理上，高錳酸鉀活化之錳砂具高抗菌生長潛能。

Filtration is an essential process for water treatment plant (WTP), but its filtration efficiency becomes worse as filter is blocked by contaminants such as organic and inorganic matter (e.x., colloidal particles, algae, microorganisms). During filtration, once the biofilms assembled on the filter media, the filtration ability and the filter run would significantly reduce, accompanying frequent backwashing. Therefore, it is important to delay the growth of microorganism in filtration process for sand filter operation. Quartz sand with silicate oxides is commonly used as filtration media in filtration process in WTP. It is easily attached by microorganism during filtration and the severe filter clogging induced by a large amount of biofilms forms quickly. It has been proven that metal oxides (e.x., TiO2, ZnO, MnO2) can be used as a antimicrobial material to inhibt the biofilm assembling in a nutrition-rich environment. In water treatment, manganese sand filter with MnO2 media has been widely adapted to remove the Fe and Mn ions from water for groundwater treatment plant, but its antimicrobial ability is under investigation. In this study, the antimicrobial activity of commercial manganese sand with and without KMnO4 activation was investigated to compare with the antimicrobial activity of quartz sand. Furthermore, the effect of KMnO4 and NaOCl oxidation on the antimicrobial activity of active manganese sand was studied. The lab-prepared E. coli–containing water and natural surface water with and without nutrition source (Luria-Bertani, LB) were used as a culture media. For each cultivation test, the residual microorganisms within 48 hr cultivation at 37℃ were counted by optical density (OD) method and DAPI (4',6-diamidino-2-phenylindole) staining method. The results have showed that the antimicrobial activity of manganese sand is superior to that of quartz sand. It would enhance the antimicrobial activity as manganese sand undergoes KMnO4 activation previously because the growth rate of microorganisms is delayed by increased active nano-scale MnO2 particles with high surface area on the manganese sand. In addition, the oxidation-reduction potential (ORP) in manganese sand-containing water is increased with reducing residual microorganisms. It is also found that a large amount of K+ releases from microbial cell in manganese sand-containing water after cultivation due to the occurrence of inactive microorganisms. The quantity of residual K+ in cultivated water for manganese sand with KMnO4 activation is much higher than that without KMnO4 activation. With increase in the amount of active manganese sand, the quantity of released K+ increases and the residual microorganisms decreases. On the other hand, the KMnO4 or NaOCl oxidation can not only destroy the microorganism cells in water but also increase the amount of MnO2 on the active manganese sand, which substantially reduce residual microorganisms in water. However, the optimum improvement in antimicrobial ability of manganese sand can be achieved by KMnO4 oxidation due to its strong inactivation ability to microorganisms and the occurrence of much more MnO2 on KMnO4-oxidized manganese sand than that on NaOCl-oxidized manganese sand. The result has indicated that commercial manganese sand with KMnO4 activation has a high antimicrobial growth potential for drinking water treatment.